The rotary nozzle has been widely used as a device for adjusting the quantity of molten steel, in an appliance such as a ladle for carrying molten steel discharged from a steel converter or pouring into a mold, or a tundish for receiving molten steel from the ladle and pouring into a mold. In a rotary nozzle 25 conventionally used, as shown in FIGS. 3, 4, a fixed plate brick 2a is fixed in a concave portion 17 of an upper case 15 mounted on a base plate 10 installed on the bottom 9 of a ladle 8. A sliding plate brick 3a is fixed in a concave portion 18 of a lower case 16 capable of rotating.
A nozzle hole 4a is made in the fixed plate brick 2a and,the fixed plate brick 2a is fixed to the upper case 15 at a position in which the hole 4a matches with a nozzle hole 13 in the upper nozzle 11. Nozzle holes 5b, 5c are made in the sliding plate brick 3a and the sliding plate brick 3a is fixed to the lower case 16 at a position in which the holes 5b, 5c match with nozzle holes 14, 14a in the lower nozzles 12, 12a. As shown in FIG. 3, a gear 19 is provided on the outer peripheral portion of the head portion of the lower case 16 which fixes the sliding plate brick 3a and this gear 19 is meshed with a gear 21 of a reducer 20 installed on the bottom 9 of the ladle 8, so that the sliding plate brick 3a is rotated by a drive motor 22 used as a drive power, sliding on a fixed plate brick face 2a while maintaining a contact force to the fixed plate brick 2a. 
Thus, molten steel flows from the nozzle hole 13 in the upper nozzle 11 into the nozzle hole 4a in the fixed plate brick 2a as indicated with an arrow in FIG. 4. The sliding plate brick 3a rotates up to a position in which either of the nozzle hole 5b and the nozzle hole 5c in the sliding plate brick 3a and thus either of the nozzle holes 14 and 14a in the lower nozzles 12, 12a matches with the nozzle hole 4a in the fixed plate brick 2a, and the molten steel flows further and is poured.
As for control of the pouring amount of molten steel, as shown in FIGS. 5a, 5b, as the rotation starts, the nozzle hole 5b in the sliding plate brick 3a and the nozzle hole 14 in the lower nozzle 12 deviate from the nozzle hole 13 in the upper nozzle 11 and the nozzle hole 4a in the fixed plate brick 2a so that an opening portion 23 narrows gradually. As the sliding plate brick 3a rotates further, the nozzle hole 4a in the fixed plate brick 2a is closed as shown in FIGS. 6a, 6b and the nozzle hole 4a remains closed completely until the sliding plate brick 3a rotates further so that the nozzle hole 5b in the sliding plate brick 3a meets with the nozzle hole 4a in the fixed plate brick 2a. As a result, discharge of molten steel from the ladle is stopped temporarily. In this way, the rotary nozzle repeats its sliding rotation to adjust the discharge amount of molten steel.
Since the fixed plate brick and the sliding plate brick of a conventional rotary nozzle are damaged due to melting by a passage of high temperature molten steel during this sliding rotation, there is a fear that molten steel may leak. Therefore, both the bricks have been handled as consumable parts which must be replaced periodically. However, because the fixed plate brick and the sliding plate brick are expensive, it has been indispensable to study about the configuration and structure which enables its durability to be improved to extend the replacement cycle as long as possible. Thus, as a related art , an invention of Japanese Patent Application No. 327897 (rotary nozzle brick body and rotary nozzle) (hereinafter referred to as the conventional invention) was made and has been well known.
The above-described conventional invention intends to reduce cost by forming the brick body composed of the fixed plate brick and sliding plate brick into a reasonable and economical shape. Reduction of cost is actually achieved by forming into a substantially egg-like shape in its planview. However, the substantially egg-like shape reduces the contact area when the sliding plate brick is in a half opened state or in a transition from the half-opened state to a full-opened state during rotation, so that the contact distance between the fixed plate brick and the sliding plate brick decreases. As a consequence,a probability of molten steel leakage outside through that location has been recognized as a critical issue in practice
Accordingly an object of the present invention is to obtain a fixed plate brick and sliding plate brick having a reasonable shape by forming into a shape free of problems about leakage and durability in order to eliminate leakage for safety and improve cost matter relating to the durability.